Millivolt control unit



J. W. ALDERSON Filed Aug. 10, 1943 MILLIVOLT CONTROL UNIT Jan. 25, 1949.`

Patented Jan. 25, 1949 MILLIVOLT CONTROL UNIT John W. Alderson, oakland, Calif., assigner it ther United States of America, as represented by the Secretary of War Application August 1o, 1949, serial No. 498,049

4 claims. (01915-119) (Granted under the act of March 3, 18.83, as amended April 30, 1928; 370 0. G. 757).-`

The invention described herein may be manufactured and used by or for the Government for governmental purposes, Without the payment to me of any royalty thereon.

This invention relates to remote control systems, and more particularly to improvements in such systems employing electron discharge devices.

Remote control devices for communication vapparatus must be sensitive and at the same time unaffected by high amplitude noise transients. Sensitivity is desired for providing accuracy at high speed. A

It is an object of this invention to provide a unit for remotely controlling positively and efflciently electrical systems including radio transmitters and receivers.

A further object is the provision of a remote control device for electrical apparatus and the like, which device includes a gas lled'tetrode electron discharge tube which may be controlled by voltage received from an automatic volume control circuit of a radio receiver.

A further object is the provision of a remote control device of high sensitivity, unaffected by transient disturbances, and controllable by very small voltages.

` In accordance with the specic example of the invention chosen for illustration in Fig. 1, a transmitter 'at a control site emits definite signals which affect the automatic 'volume control circuit of an ordinary radiok receiver remotely positioned at the site of theV apparatus being controlled. The automatic volume control circuit is connected and its output transmitted to the grid of a gas filled tetrode electron discharge tube, which is biased near its striking voltage, so that very slight variations in the voltage of the automatic volume control circuit will control the operation of the tube. i

causes an interruption ofthe plate current flow for half-cycle `periods of the alternating plate voltage. This type of tubeas the parameters are here organized is Vsensitive to minute voltage changes in the grid circuit. tube is positive; the cathode anode circuit will conduct or cease to conduct depending onthe polarity of the applied grid voltage.

Fig. 1 shows the-circuits of one form of the invention which has been successful, and vthe following description thereof is given as anv e'xy vif desired, by transmitting voice action or the like in such manner as to produce a denite volume output. Examples of use of an audio output are seen in patents to Edwards et al., 1,968,750, July 31, 1931; Tice, 2,356,364, August 22, 1944; and Frederickson, 2,158,809, May 2, 1939.

The disclosurefherein is'su'icient to indicate that by utilization of the automatic volume control a steadypotentialmay be maintained by proper transmission yto thereceiver, with a resultant drop by a change signal keyed from a transmitter to the receiver. Y But likewise, if the tube I is arranged to be normally critically biased to non-conduction, the tube '6 may be normally conducting, holding a relay closed, and lresponse effected by keying or otherwise producing a signal of raised voltage to the grid 2 whereby the tube These and *other objects'are attainedloy the arrangement and combination of elements hereinafter described'and illustrated in the accompanying drawings, forming a part hereof, and in which Fig. 1 is a diagram of a circuit embodying the invention.

' Fig. 2 is a diagram of another circuit showin an application of the invention.

Referring to the drawings, the remote control device is shown to include a gas filled tetrode tube I, having a grid 2 connected through an inductance L to the negative terminal of an automatic volume control circuit of an ordinary radio receiver, The gas filled tetrode tube is of the hot cathode type, which requires a definite grid voltage, called the striking or starting'voltage, in order to cause the flow of plate current. In the tubes herein described the plate voltage is supplied by an alternating current source, which` I will be caused to conduct, and the'tube 6 cut off by the resulting sharp drop at the gas tube plate due to the characteristicl abrupt discharge action inagas tube. Y

Bridging the lower and upper positive and'neg-v atlve terminals of the input circuit from the radio receiver to my remote control devicethere is a potentiometer high first resistance 5I, about i'lve megohms, and inparallel with the major lower part thereof from the brush of the potentiometerthere is a second resistance 52 of about two megohms, its upper' end connected to the brush of the potentiometer. This brush is connected directly to the control grid 2. The lower ends of the resistances 5| andV 52 are-connected to the brush of a variable vresistance 53'of about 1,000 ohms, which is connected at its ends in'series betweenthe cathode 3 of tube Iv andthe left end of the' secondary of a transformer T, and similarly connected in parallel to thisfresistor there is a fourth resistance 5,4 of about 500 ohms, so that the resistances 53-54 form a series-parallel xed resistance in the cathode lead from the transformer. The plateior the tube Imis con- The action of they nected tfthe' opposite end of the secondary-with a fifth resistor 55 of about 25,000 ohms connected between the cathode lead and the plate lead or means of the potentiometer."resistance 5,!the

negative bias of the grid 2--due to the normal potentials of the AVC leads and the drop across resistors 5| and 52-may be controlled'andadjusted to a required critical condition, and that throughout such adjustment the effective resistance acrossv the-line will: never--be-less than one megohm; so that current consumption.` isf measured in-f mieroamperes. These two resistors -will also-serve as a gridleak forany tendency for excess change of Abiasi-tobui-ld uponfthe-grid. Resistors 53 andy-,55l with the brushcontact from resistor 52, `serving together as -a potentiometer enable adjustment therefto utilize the transformer secondary outputtoaidinestablishing a proper grid potential level in relation -to the cathode and `Tlf1earrangementisalso such -that small plate current'wi-ll flow When-the-jtube yI is energized, but-the potenti-al `fluctuations; at the plateupon signal functioningfof the grid- 2 willbe large` and. suiicientto produce wide extremes Vof conduction inthe tube Gfwhen imposed-on the grid of the latter. The resistance-Siserves 4additionally as agridleakattube 6.v y t A tube-ii whichrmay beefthe 6L6l type has its grid 1 biasedbythe-plate cireuitfof tube i, and theL ilowjof cur-rentin the.- plate-circuit of tube 6 operates arelay R.,l f

-Inoperation, keying 'or' controlling potential from the automatic: volumecontrol/applied to the inputV circuit of the tube-l A`need( not exceed one volt directy current. `and for thief-reason theV cur'- rentconsumption fis-measured in nfri'croamperes. The reactance--I;Y-(Whiclr may be h in this instance) is provid-edito eliminate alternating voltage from the'jexternal---control voltage circuit. Such voltagefmaybe parasitic, 'originating in the receiver or-otlaer-wise.Y

In a first instance,- theresistance' 53 is adjusted to the point at Whichthestrikingorfstarting voltage is produced to cause ionization-in the gas lled tube, and causea'nuni-directional current to flow. This-j action results-in a Vvoltage drop across- 56. Condenser-- EL maintainsthe unidiating grid voltage; during'l whalf cycle when the alternating current voltage taken from the left `end of the secondary of the transformer T and applied togrid 2 is negative, the right end of the secondary of the transformer T applies an alternating current voltage to the plate, which is positive, Since the grid;2 is negatively biased just below the Vstriking voltage, no plate current will now. VI-lowever,v bykeying the transmitter so as t0 develop suflicient voltage from the automatic volume control circuit to bias the grid 2 to the striking Aveltagepa plate to cathode current will beiicaused .toffiow'.. On the next half cycle, the

Y cal. potentialr-on theggrid.- .'WhenitisldesiredQto alter :the Vcondition, and operate tlie. relay asignal is. keyed at the Vtransmitter,causing thelowering of potential supplied to the grid .Zilfro'mthef AVC and. raising. that of Ythe `cathode, with ,the

Y result that tube. I` is.,.cut,oi`iandathetuhe il is,

brought `into conduction, its. plate current. picking up the relay. e e, y]

If .the V`tube vii is to.normallyoperate, keeping the relay picked up, the adjnstmentiot the second case above described isima'de,,thetAVOoutput stabilized to maintain .the .tube ll`..cutoff, .andato effect controlI actionthesignal transmittedmould be of such natureasI-to .cause the AVGto increase the potential .at grid...2v .relativeto .the cathode,

, l when the-tube [would be red',.cutting;.o tube.

rectional current at a sulcientfconstant value keeping theftube 6 out oit.v .Con-trollingwiu resuit if asom-'ceci` low voltage direct, current properly polarized isapplied' tc-the vinput terminalsof the gas-lled tetrode; tube cutting off the Ylatter-andl ring tube 6;, with consequentpick upfof the relay R.l Y y In a 'second case, `by adjusting resistance' 5-l'-to a certain value, the grid 2v-oi the tubel I- Ycan be biased negatively to suchfan extent as to prevent initiation of the new-of the :plate current in tube I', with the result that there will be -njo Voltage dropover resistance 56,-thusremovingv the negative bias on the :grid of tube 6- an'd allowing-plateA current to flow intube-6v-toactuate a'relay, -or other devicei `In this case, ifea lowV voltage direct cur-rent of proper polarityfor amplitude vhigher in a small degree than that at .which the normal: grid voperation i'sadiustedis ,applied across-'the grid andv cathode 'oi tube I, the latter will be fired, cuttingv off tube'end dropping .the r'elayR.Y

In' the secondcase, Without the required operf B anddroppingtliefrelayr In the device of Fig. l, input con-trol Aunit should beiwired directly totthe voutputof the automatic volume .control Vcircuitcithe receiyer,.as shown tv-here,l usually;-ilteringf action.has alread.y taken` place., The -delayedaac'-- tion Aof 4the filtered :automatic volumev control will reducehigh amplitude noisetransientsto-a valuethat Will not interferewith normal Vkey'ing,and

, control: .can beA accomplished .through-.noise loud-v enough Yto render other control systems inoperative, y, :i In Fig. I. .the is Vshown..controlling atube 6 which; controls fa.. relay..V For. .fast key-ingsistance 56 should be not more thanf50,000ohms and capacitor llil not more ythan .lV vxvnicrofara.dr.1

Eig. 2 .the unitis. `sliown .controlli-ng Aa relay. and an. oscillator or buffer :tuba-,Jorlar1y-ki-nd :or electron discharge ,tu-be. The controlled ltul: el,|

- receives its bias to cut-off directly from thefvolt-f ageacrossresistance 56 f y r-y The transformer T applies an alternatingcurl rent. potential bto the plate Yof vtube I., and asf a result the potential tof: plate isis negative-every,

-f otherlialf.r cycle, which stopstthe .operationmf tube l duringfthe-half` cycle period. Howevendue to .the actionof. condenser( Gylgcurrent flow tothe grid of tube. 6 will not ybe interruptedfuntil current. flow in tube. l isdiscontinuedby negati-ve biasing action; orgrthef tubefcan liearranged fto he norm;

mally inactive, and placed in operation by keying 'vaiuewhich produces tneifstrikir'ig bias orvoice action to bias thezgridabgve thestriking age on grid '2. Now,'"'a`ssurning"; receiver isreceiving a carrier' 'of'.ja deidniteirequency' transmitted fromV aVV remote cotr'ol `"site, a potential change appears in the automatic volume control circuit of the radio receiver. An operator at the remote control site keys a transmitter to send out the carrier to vary the automatic volume control voltage and vary the grid bias voltage on tube I to obtain the striking voltage or t deviate from the striking voltage, as may be desired,

Where remote control by radio is desired the necessary keying voltage is obtained from-a receiver tuned to the frequency of the controlling carrier. The automatic volume control circuit of the receiver provides more than sufficient voltage to operate the control unit on even the weakest of signals. The sensitivity of the control unit is less than one-half volt at a current drain of a few microamperes. The low voltage required and the extremely small current drain results in very little disturbance to the normalvfunction of the automatic volume control system in the receiver.

operated by a key or the like. Systems already installed and operated by remote control wire lines can utilize the control unit to advantage. Several independent functions can be performed using only one pair of wires with positive results and with very low potentials. The device is adapted for use with radio or wire repeater apparatus, utilizing a single carrier or a carrier of multi-tone modulation. It can also be Well used with high speed telegraphy or teletypewriting control of single or multiple apparatus for single or repeater operation. Other uses include high speed control of automatic tape recorders and senders, code or telegraph apparatus, electronic ormechanical control of apparatus of any kind, locally or by remote control, and use as an indicator or warning device or an overload or underload relay.

The above description is to be considered illustrative and not limitative of the invention Obviously, numerous modications and applications can be made without departing from thespirit lof the invention as set forth in the appended claims. The invention having been described, what is claimed is:

. l. In a remote control system comprising a radio transmitter, a remote radio receiver wherein incident modulated radiations from the transmitter are converted into a unidirectional current output, a device to be controlled remote from the transmitter and remote from the receiver, and a control device operative by variation in said unidirectional current output operatively connected to said device to be controlled; the improvement in said control device which comprises a gas-charged thermionic tube having at least an anode, a cathode and a control grid, first and second input leads from the unidirectional output of said receiver, a variable first resistor and a parallel second resistor of half the value of the first connected commonly between the grid and said i'lrst input lead, said first resistance bridging said leads and the grid having brush connection -named fth resistor and the anode, an alternating current anode supply having one terminal connected between the fifth and sixth resistors so that the sixth resistor and capacitor are in series parallel with the source and anode, another terminal of said source being connected at the outer ends of the said third and fourth resistors so that the latter are in series parallel with the source and cathode, and so that the third and fourth resistors at one side and the fifth resistor at the other are in series across the line with said source, a second thermionic tube having at least an anode, a cathode and a control grid, an anodecathode current supply connected to said second tube, a current-operated part of the Said device to be operated being connected in said anodecathode circuit, the grid of the second tube being connected to the anode of the rst tube, said variable resistors being adjusted to establish a grid-cathode relation critically near the potentials V for ring the tube.

2. In a remote control system comprising a radio transmitter, a remote radio receiver wherein incident modulated radiations from the transmitter are converted into a, unidirectional current output, a device to be controlled remote from the transmitter and remote from the receiver, and a control device operative -by variation in said unidirectional current output operatively connected. to said device to be controlled; the improvement in said control device which comprises a gas-charged thermionic tube having at least an anode, a cathode and a control grid, first and second input leads from the unidirectional output of said receiver, a high potentiometer resistance across the line of said unidirectional current, a brush connection between the grid and said resistance, an alternating current anode source connected at one terminal with the anode, an

anode resistance and a condensor in series parallel between the source and anode, a resistance bridging the output of said source, a tap connection between the last named resistance and the cathode, a brush contact between the grid and the last name resistance, a second thermionic tube having at least an anode, a cathode and a control grid, an anode-cathode current supply connected to said second tube, a current-operated part of said device to be operated being connected in said anode-cathode curcuit, the grid of the second tube being connected to the anode of the iirst tube, said connections between the grid of the iirst tube and resistors being adjusted to establish a grid-cathode-anode relation in the i-irst tube criticallynear the potentials for iiring of the tube. j

3. The structure of claim 3, wherein a suppressor grid is included in said first tube having ya k permanent negative potential vrelative to the therewith, a variable third resistor connected in JOI-IN' W. ALDERSON. 3

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